Method for setting a multiplication of a continuously variable automatic transmission equipped with a variator

ABSTRACT

A method for setting a multiplication of a continuously variable automatic transmission (CVT transmission) comprises the following steps: 
     a) it is determined in a test module (M 1,  M 1′ ) whether an operating situation is present in which a program module (M 2,  M 2′ ) for adapting an existing transmission multiplication (i_v_ist) to a vehicle speed (v_F) or to an output rotational speed (n_ab) of the transmission is activated; in the negative a transmission specified multiplication (i_v_stratagy, i_v_start) is determined as new transmission specified multiplication (i_v_soll) from a characteristic field for a regular driving strategy; 
     b) it is tested in the program module (M 2,  M 2′ ) whether the vehicle speed (v_F) or the output rotational speed (n_ab) of the transmission is higher than a predetermined limiting value (v_F_limit, n_ab_limit); 
     c) in the case of a positive inquiry, a predefined transmission specified multiplication (i_v_ABS, i_start_w) assigned to the determined operating state is set as new transmission specified multiplication (i_v_soll) when the starting clutch is activated; in the case of a negative inquiry, a processing function (F 4,  F 17 ) is begun in order at least partly open a starting clutch and the transmission specified multiplication (i_v_ABS, i_start_w) assigned to the determined operating state is set as a new transmission specified multiplication (i_v_soll).

FIELD OF THE INVENTION

The invention relates to a method for setting a multiplication of acontinuously variable automatic transmission (CVT) equipped with avariator for a vehicle having an electronic transmission control (EGS)which has a control unit, with a microcomputer connected with sensorsand/or external control units to detect several operating parameters,and with an actuator wherein a starting clutch is actuatable by theactuator.

BACKGROUND OF THE INVENTION

From the practice methods are known for adjusting the multiplication ofan automatic transmission in which, on the basis of specific inputvariables on the electronic transmission control (EGS), such asaccelerator pedal position, motor rotational speed, rotational speeds ofprimary and secondary disks of a variator and the like, the transmissionmultiplication is set by means of characteristic fields stored in theEGS for a driving strategy under usual operating conditions.

For multi-step automatic transmissions, there are also known from thepractice, special programs for particular operating conditions such as awinter driving program manually actuatable by the driver, via a switch,for better starting with low friction values, i.e. a snow-covered oriced road. Hereby is prevented, among other things, shifting in thelowest gear as a starting multiplication.

The known winter driving program, however, cannot be used in automatictransmissions having a variator, since the multiplication range of thetransmissions is substantially limited by the mechanical stops of thepushing linked band of the variator with the shortest possiblemultiplication (LOW) and longest possible multiplication (overdrive,OD). Compared to multi-step automatic transmissions CVT transmissionsusually have a larger spread accordingly making shorter startingmultiplications possible, which nonetheless are a cause of low startingpower and poor starting stability in the presence of low road frictionvalues.

Besides, it has proven problematic in automatic transmissions having avariator that at extreme retardations of the driving speed, such asemergency braking or engagement of an antiblock system (ABS), thesetting of the multiplication is so slow that when an accelerationoperation immediately follows braking, there is not an optimummultiplication of the transmission.

The starting power when restarting is accordingly weak as a result of astill too low multiplication ratio. In addition, during an extremeretardation of the driving speed, there appear on the drive train highdrag torques which impair the driving stability of the vehicle.

Therefore, this invention is based on the problem of making available amethod which makes possible a quick adaptation of the multiplication ofan automatic transmission with a variator (CVT transmission) to acritical driving situation, mainly in the cases of low road frictionvalues and abrupt decelerations, a strong starting power being ensured,and at the same time the drag torques of the drive train can be reducedwhereby, in turn, a high braking stability of the vehicle is ensured.

SUMMARY OF THE INVENTION

With the aid of the inventive method, which can be implemented in aregular driving strategy, a free multiplication adjustment isadvantageously possible for setting a multiplication adapted to the needwhen starting a motor vehicle or when restarting after a strong brakeoperation.

By opening the starting clutch, the variator is uncoupled from the motoror the output and, in this manner at least, an additional degree offreedom is obtained.

The action of the inventive method is, in particular, dependent on thetransmission type, i.e. on whether the starting clutch that conveys thepower flow for forward drive is situated in the transmission on thesecondary side, hence on the output side, or on the primary side andthus on the motor side.

If the starting clutch is on the secondary side of the variator, thelatter is uncoupled from the output and the wheels when the startingclutch is opened.

Thereby the drag torques of the part of the drive train connected withthe wheel are advantageously reduced when decelerating, and the variatorcan be adjusted, independent of the output rotational speed, to amultiplication suitable to an actual vehicle speed, with which it ispossible to continue driving after having applied the inventive method.

The use of the inventive method in the arrangement of the forcelockingforward shifting and starting clutches on the secondary side provesespecially advantageous when the variator is adjusted while the vehicleis parked. The variator, which runs at the motor rotational speed, can,of course, be easily adjusted when the starting clutch is completely orat least partly open during a stopped adjustment of the variator andwhen the variator is uncoupled from the wheel rotational speed.

The circumstance described precisely predestines the inventive method,e.g. for a manually selectable winter program with a presetting of themultiplication prior to starting with a low road friction value, wherebythe starting power and the starting stability are considerably improved.

The inventive method, however, is also adequate for other applications.It is very advantageous in braking operations with a sharp reduction ofthe vehicle speed, as in an engagement of an antiblock system (ABS).

It is also possible, by the inventive method, to superimpose a regulardriving strategy to improve the driving stability of the vehicle, thevariator being separated from the output or wheel by the opening of thestarting clutch.

Thus the drag torques of the drive train can be effectively reduced andthe variator can correspondingly be freely set to the multiplicationsuited to the actual vehicle speed or the output rotational speed of thetransmission, with such multiplication driving is continued afterterminating the program.

The advantages of the inventive method are optimally prevalent incombination with an arrangement of the starting clutch on the secondaryside.

However, the inventive method also has advantages when the startingclutch is disposed on the primary side of the variator, e.g. in theabove described situation of an ABS engagement.

The variator here remains connected with the output or wheel. Theadjustment in the direction of the longest possible multiplication (OD)reduces the slowness of the drive train connected with the wheel. Byopening the starting clutch, the variator is uncoupled from the motorwhereby the drag torques of the drive train are advantageously furtherreduced.

In addition, via a function within the electronic motor control, themotor can advantageously be guided to a defined rotational speed inorder to ensure the oil supply for a quick variator adjustment. Thisadvantage results from a transmission oil pump operated at the motorrotational speed, since a higher motor rotational speed results in aquicker pressure build up.

The inventive method constitutes a universally useful program module foran automatic transmission, it is particularly adequate for a CVTtransmission with a belt drive variator, but it obviously can also beused in automatic transmissions with different types of variators.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantageous embodiments and further developments of the invention willnow be described with reference to the drawings in which:

FIG. 1 is a flow chart of a method for setting a multiplication of a CVTtransmission with sharp reduction of the vehicle speed;

FIG. 2 is a flow chart of a method for setting a multiplication of a CVTtransmission with a winter driving strategy wherein a startingmultiplication is set;

FIG. 3 is a schematized representation of the curve of a multiplicationi_v according to the vehicle speed v_F or to the output rotational speedn_ab in a braking operation; and

FIG. 4 is a schematized representation of the curve of themultiplication i_v according to the vehicle speed v_F or to the outputspeed n_ab when using a winter starting control.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, in each is shown a flow chart of a methodfor setting a multiplication of a CVT transmission of a motor vehiclewith a starting clutch on the output side.

In a first test module M1, M1′, each is determined by comparison ofinput signals on a control unit of an electronic transmission controlwith predefined characteristic data, whether a predefined operatingsituation exists in which a program module M2, M2′ for adapting anexisting transmission multiplication i_v_ist to a vehicle speed v_F orto an output rotational speed n_ab of the transmission is activated.

If this is not the case, in a processing function F6, F9 or F15 atransmission specified multiplication i_v_strategy or i_v start isdetermined from a characteristic field as a new transmission specifiedmultiplication i_v_soll for a regular driving strategy.

In the subsequent program module M2, M2′ for adapting the transmissionspecified multiplication i_v_soll, in a first differentiation functionF2 or F16 is tested whether a vehicle speed v_F or the output rotationalspeed n_ab of the transmission is higher than a preset limiting valuev_F_limit or n_ab_limit.

If the inquiry of the differentiation function F2 or F16 is positive,with the starting clutch closed, a predefined transmission specifiedmultiplication i_v_ABS or i_start_w assigned to the detected operationstate is set as the new transmission specified multiplication(i_v_soll).

With a negative inquiry, a processing function F4 or F17 to open thestarting clutch is started and to the transmission specifiedmultiplication i_v_ABS or i_start_w is assigned to the operation stateand set as the new transmission specified multiplication i_v_soll.

In the embodiment of FIG. 1, in the first test module M1 is determinedthe predefined operating situation for activating the program module M2,provided for adaptation of the transmission specified multiplication,which is a predefined reduction of the vehicle speed dv_F/dt or of theoutput rotational speed dn_ab/dt of the transmission.

As can be seen in FIG. 1, in the first test module M1, firstdifferentiation function F1 tests if a signal “ABS active”, i.e. thatABS braking exists, has been issued via a CAN bus to the control unitfrom the ABS control as an external control unit.

The test module M2 is started if the inquiry is positive.

If the inquiry of differentiation function F1 is negative in test moduleM1, another differentiation function F5 is started to test whether abrake of the vehicle is actuated.

In the presence of an antiblock system, a gain in time is achieved inABS braking, since adjustment of the transmission specifiedmultiplication i_v_soll has been effected without finishing other testfunctions and calculations.

However, with differentiation function F5, which in this case is coupledwith a brake light or brake pressure switch, a strong deceleration isalso detected in the absence of an antiblock system or in the case of adefective ABS control.

To detect a strong braking operation, a sensor can also be provided onthe output shaft, such sensor senses braking as a rotational speedreduction and relays it to the control unit.

In case no deceleration has been detected in differentiation functionF5, a processing module F6 is started to adapt the transmissionspecified multiplication i_v_soll to a preset, regular transmissionmultiplication, i_v_strategy, the test module M1 being restarted afterfinishing or interruption of the processing module F6.

The preset transmission multiplication i_v_strategy corresponds to thetransmission multiplication during normal driving operation, which inthe electronic transmission control EGS is stored in a characteristicfield, and corresponds to the actual vehicle speed or to the inputspeed.

In differentiation function F5, if a deceleration is detected, a testfunction F7 is started to determine whether the reduction of the vehiclespeed dv_F/dt or the output rotational speed dn_ab/dt of thetransmission is less than a limiting value (dv_F/dt)_limit or(dn_ab/dt)_limit stored in a characteristic field, wherein(dv_F/dt)_limit=f(v_F) or (dn_ab/dt)_limit=f(n_ab) applies.

The retardation is calculated in the EGS so that the method can also beused in this way without an ABS system.

In case of a negative inquiry from the test function F7, the processingfunction F6 is started, to adapt the specified multiplication i_v_sollto the preset, regular transmission multiplication i_v_strategy andafter finishing or interruption of the processing function F6, the testmodule M1 is activated again.

If the test module F6 delivers a positive inquiry, the test module M2 isstarted, the method applied in the above described manner.

In differentiation function F2 of the test module M2, if it is actuallydetected that the vehicle speed v_F or the output rotational speed n_abof the transmission is not higher than the preset limiting value whichcorresponds to a lower vehicle speed or output rotational speed, aprocessing function F4 is started to open the starting clutch, and thetransmission specified multiplication i_v_soll, with uncoupled variator,is adjusted in a processing function F3 to a transmission specifiedmultiplication for ABS braking i_v_ABS.

After setting the transmission specified multiplication for ABS brakingor interruption of the processing function F3, the test module M1 isreturned to.

In a positive inquiry of the differentiation function F2, i.e. that thevehicle speed v_F or the output rotational speed n_ab of thetransmission is higher than the preset limiting value, the processingmodule F3 is immediately started to set the transmission multiplicationi_v_ABS and finished when the starting clutch is closed so that themultiplication of the transmission or of the variator is adjusted whenthe drive train is closed.

FIG. 3 shows for an ABS deceleration a schematized representation of aqualitative curve of the multiplication i_v according to the vehiclespeed v_F or to the output rotational speed n_ab. In an operating pointB before the deceleration, first lies a multiplication i_v_B at avehicle speed v_F_B. Immediately before the deceleration, correspondingto the driver's withdrawal of the acceleration pedal, the multiplicationis adjusted while the vehicle rolls in the direction of i_OD, since theleast drag torques are present in the drive train with themultiplication when the starting clutch is closed.

During ABS deceleration, the multiplication i_v is adjusted along apredetermined characteristic line up to a vehicle speed v_limit whichrepresents a limiting value at an operating point A with an appertainingmultiplication i_v_A. The starting clutch is still closed. When reachingthe operating point A, the variator is separated on the output side,i.e. the starting clutch situated on the secondary side of the variatoris opened. In this state, the variator that turns at the rotationalspeed of the motor can be moved to the starting multiplication i_start.

FIG. 2 shows a flow chart of a variant of the method shown in FIG. 1,wherein the predefined operating situation in the first test module M1′to activate the program module M2′ represents a start with low roadfriction value and the activation of a “winter drive strategy”.

In the first test module M1′, in a first differentiation function F8, itis correspondingly tested whether the control unit has detected if aswitch “winter drive strategy” has been activated.

In the instant embodiment, a driver can manually dial the winter drivestrategy before the loose driving, via a switch. When this is the case,another differentiation function F14 is activated to determine whetherthe existing transmission multiplication i_v_ist is higher than a winterdrive multiplication i_start_w assigned to the operation state found. Inthe negative, in the processing function F15 the winter startingmultiplication i_start_w is determined as normal starting multiplicationi_start.

When the differentiation function F8 delivers the result that the switch“winter drive strategy” is not actuated, there is determined in theprocessing function F9 as the normal starting multiplication i_start theshortest possible multiplication i_LOW, and in a differentiationfunction F11 is tested whether the vehicle speed v_F or the outputrotational speed n_ab of the transmission is lower than a predeterminedlimiting value v_limit or n_ab_limit.

If this is proven correct, another differentiation function F12 isstarted to test whether the existing multiplication i_v_ist is higherthan the normal starting multiplication i_start.

When the vehicle speed v_F or the output rotational speed n_ab of thetransmission is higher than the limiting value v_limit or n_ab_limit, orwhen the transmission specified multiplication i_v_ist is lower than thenormal starting multiplication i_start, the first test module M1′ isreturned to.

However, if the existing transmission multiplication i_v_ist is higherthan the normal starting multiplication i_start, the normal startingmultiplication i_start is set as the transmission specifiedmultiplication i_v_soll before returning to the test module M1′.

The winter starting multiplication i_start_w of the transmissionconstitutes a discrete value which is between the shortest possible andthus highest multiplication i_LOW and the longest multiplication i_OD ofthe transmission, i.e. between the mechanical stops of the variator.

It is thus ensured that with low road friction values the lowermultiplication i_start_w is started in order, e.g. to prevent a spinningof the wheels on a smooth foundation. The winter drive control ismanually dialed by the driver of the vehicle via a switch in theinterior of the vehicle.

FIG. 4 makes clear the action of the method according to FIG. 2 whenactuating the switch “winter drive strategy” and shows a schematizedrepresentation of the curve of the multiplication i_v according to thevehicle speed v_F or the output rotational speed n_ab.

If the driver activates the winter drive strategy while the vehicle doesnot moving, the winter drive multiplication i_start_w, latently storedin the electronic transmission control, is set by a parking adjustmentof the variator. When the switch “winter drive strategy” is deactivatedprior to starting, the variator is, in turn, uncoupled from the outputand the normal start multiplication i_LOW is set.

When the switch “winter drive strategy” is activated at an operatingpoint C in which the existing multiplication i_v_C is higher than thewinter start multiplication i_start_w, and the vehicle speed is lowerthan a limiting speed v_limit, the starting clutch is likewise openedand the variator adjusted to the winter start multiplication i_start_w.

In the instant embodiments, the multiplication in the ABS decelerationor the winter drive strategy is freely adjusted in discrete values, butthe free multiplications to be set can also be variably formed by theelectronic transmission control, e.g. in combination with a fuzzy-logicprogramming departing from the actual operating parameters.

Reference designations F2, F5, F7, F8. F11, differentiation functionF12, F14, F16 F3, F4, F6, F9, F13, processing function F15, F17, F18i_start start multiplication i_start_w winter start multiplication i_LOWshortest possible multiplication i_OD longest possible multiplication,overdrive i_v_ist multiplication of the transmission i_v_A, i_v_B,multiplication at the A, B, C operating point i_v_C i_v_ABSmultiplication during an ABS deceleration i_v_soll transmissionspecified multiplication i_v_strategy multiplication of the “normal” or“regular” driving strategy M1, M1′, M2, M2′ program module, test modulen_ab output rotational speed of the transmission n_ab_A, n_ab_B outputrotational speed at the operating point A, n_ab_C B, or C dn_ab/dtretardation of the output rotational speed (dn_ab/dt)_limit limitingvalue of the retardation of the output rotational speed v_F vehiclespeed v_F _A, v_F _B, vehicle speed at the operating point v_F _C A. B.C V_limit limiting value of the vehicle speed dv_F/dt reduction ofvehicle speed (dv_F/dt)_limit limiting value of the retardation of thevehicle speed

I claim:
 1. A method carried out by an electronic transmission controlfor setting a multiplication of a continuously variable automatictransmission having a variator (CVT transmission) for a motor vehiclehaving the electronic transmission control, said control having acontrol unit with a microcomputer connected with one of sensors andexternal control units to detect several operating parameters and withan actuator wherein a starting clutch is actuatable by the actuator,said method comprising the following steps: a) determining in a testmodule (M1 or M1′), by comparison of a set of input signals in thecontrol unit with a predefined characteristic data, if a predefinedoperating situation exists in which a program module (M2 or M2′) isactivated for adaptation of an existing transmission multiplication(i_v_ist) to one of a vehicle speed (v_F) and an output rotational speed(n_ab) of the transmission; and determining in the negative, in aprocessing function (F6, F9 or F15 respectively), a transmissionspecified multiplication (i_v_strategy, i_v_start) from a characteristicfield as a new transmission specified multiplication (i_v_soll) for aregular driving strategy; b) in the program module (M2 or M2′) foradaptation of the transmission specified multiplication (i_v_soll),testing in a differentiation function (F2 or F16) if one of the vehiclespeed (v_F) and the output rotational speed (n_ab) of the transmissionis higher than a predetermined limitation value (v_F_limit, n_ab_limit);and c) for a positive inquiry of the differentiation function (F2 orF16), and when the starting clutch is closed, assigning a predefinedtransmission specified multiplication (i_v_ABS), i_start_w) to adetected operation state and setting the predefined transmissionspecified multiplication (i_v_ABS), i_start_w) as the new transmissionspecified multiplication (i_v_soll); in case of negative inquiry aprocessing function (F4 or F17), starting to at least partly open thestarting clutch and assigning to the operating state the predefinedtransmission specified multiplication (i_v_ABS, i_start_w) and settingthe transmission specified multiplication (i_v_ABS, i_start_w) as thenew transmission specified multiplication (i_v_soll).
 2. The methodaccording to claim 1, further comprising the following step: in thefirst test module (M1) for activating the program module (M2) and foradaptation of the transmission specified multiplication (i_v_soll),determining for the predefined operating situation as one of apredefined reduction of the vehicle speed (dv_F/dt) and the outputrotational speed (dn_ab/dt) of the transmission.
 3. The method accordingto claim 2, further comprising the following step: in a characteristicfield of the transmission control, storing predetermined values of thenew transmission specified multiplication (i_v_soll), limiting values ofa vehicle speed reduction (((dv_F/dt)_limit)=f(v_F)), and an outputrotational speed of the transmission (((dn_ab/d) limit)=f(n_ab)).
 4. Themethod according to claim 1, further comprising the following steps: ina first differentiation function (F1) of the first test module (M1),testing whether an ABS control, as external control unit, has issued asignal “ABS active” to the control unit; and when in the affirmative,starting the program module (M2).
 5. The method according to claim 1,further comprising the following step: in the test module (M1), startingan additional differentiation function (F5) to test whether a brake ofthe vehicle is actuated.
 6. The method according to claim 5, furthercomprising the following step: in case of a negative inquiry of adifferentiation function (F1), starting the additional differentiationfunction (F5).
 7. The method according to claim 6, further comprisingthe following steps: in case of negative inquiry of the additionaldifferentiation function (F5), starting the processing function (F6) toadapt the new transmission specified multiplication (i_v_soll) to thetransmission spedified multiplication (i_v_strategy); and after one offinishing and interrupting of the processing function (F6), activatingthe test module (M1).
 8. The method according to claim 5, furthercomprising the following step: in case of positive inquiry of theadditional differentiation function (F5), starting a test function (F7)to determine if one of a vehicle speed reduction (dv_F/dt) and an outputrotational speed (dn_ab/dt) of the transmission is lower than apredetermined limiting value (((dv_F/dt_limit, (dn_ab/dt_limit)).
 9. Themethod according to claim 8, further comprising the following steps: incase of negative inquiry of the test function (F7), starting theprocessing function (F6) to adapt the new transmission specifiedmultiplication (i_v_soll) to the transmission specified multiplication(i_v_strategy_); and reactivating the test module (M1) after one offinishing and interruption of the processing function (F6).
 10. Themethod according to claim 8, further comprising the following step: incase of positive inquiry of the test function (F7), starting the programmodule (M2).
 11. The method according to claim 1, further comprising thefollowing step: activating the program module (M2′) if the predefinedoperating situation in the test module (M1′) constitutes a start withlow road friction value.
 12. The method according to claim 11, furthercomprising the following step: in a first differentiation function (F8)in the test module (M1′), testing whether the control unit detects a“winter drive strategy” switch as active.
 13. The method according toclaim 12, further comprising the following steps: in case of a positiveinquiry of the first differentiation function (F8), activating adifferentiation function (F14) to determine whether the existingtransmission multiplication (i_v_ist) is greater than a winter drivemultiplication (i_start_w) assigned to the detected operating state; andin the negative, determining the winter start multiplication (i_start_w)as a normal starting multiplication (i_start) in the processing function(F15).
 14. The method according to claim 12, further comprising thefollowing steps: in case of a negative inquiry of the firstdifferentiation function (F8), determining a smallest possiblemultiplication (i_LOW) as a normal starting multiplication (i_start) inthe proceeding function (F9); and in a coordinated differentiationfunction (F11), testing whether one of the vehicle speed(v_F) and theoutput rotational speed (n_ab) of the transmission is lower than apredetermined limiting value (v_limit, n_ab_limit).
 15. The methodaccording to claim 14, further comprising the following steps: in aninquiry of the coordinated differentiation function (F11), determiningthat one of the vehicle speed (v_F) and the output rotational speed(n_ab) of the transmission is lower than the limiting value (v_limit,n_ab_limit); and starting a differentiation function (F12) to testwhether the existing multiplication (i_v_ist) is higher than the normalstarting multiplication (i_start).
 16. The method according to claim 15,further comprising the following step: before returning to the testmodule (M1′) and in case the existing transmission specifiedmultiplication (i_v_ist) is higher than the normal startingmultiplication (i_start), setting the normal starting multiplication(i_start) as transmission specified multiplication (i_v_soll).
 17. Themethod according to claim 14, further comprising the following step: incase one of the vehicle speed (v_F) and the output rotational speed(n_ab) of the transmission is higher than one of the limiting value(v_limit, n_ab_limit) and the transmission multiplication (i_v_ist) islower than the normal starting multiplication (i_start), returning tothe first test module (M1′).
 18. The method according to claim 11,further comprising the following step: storing the predeterminedtransmission specified multiplication (i_v_ABS, i_start_w) in theelectronic transmission control as a discrete variable.
 19. The methodaccording to claim 11, further comprising the following step: in a firstdifferentiation function (F8) in the first test module (M1′), testingwhether the control unit has detected a “winter” driving state by anevaluation of driving state variables.
 20. The method according to claim19, further comprising the following step: disposing the starting clutchon a secondary side of the variator.
 21. The method according to claim1, further comprising the following step: determining that a winterstart multiplication (i_start_w) of the transmission is between ashortest possible multiplication (i_LOW) and a longest possiblemultiplication (overdrive, i_OD) of the transmission.
 22. The methodaccording to claim 1, further comprising the following step: storing thepredefined transmission specified multiplication (i_v_ABS, i_start_w inthe electronic transmission control as a discrete variable.